How to add window specific shortcuts?
For your first question regarding comments, check this out:https://meta.stackexchange.com/questions/214173/why-do-i-need-50-reputation-to-comment-what-can-i-do-instead.

To add the Space control for playing and pausing your animation in the timeline, that can be done by opening the User Preferences and going to the input tab. Find the Timeline and click the little arrow to expand it. Then click Add New to create a new shortcut. Set the control to be Keyboard and set the key to Space, then set the operator to be screen.animation_play. I found the operator by searching for AltA and using the Key Binding search, then copy pasting the operator. Since this is a timeline specific key binding, all other Space shortcuts will still work.